Many fuel injection systems for internal combustion engines use a fuel distributor for delivering fuel to fuel injectors associated with respective engine cylinders. The distributor functions to fluidically connect a supply fuel passage to each fuel injector or engine cylinder one at a time through separate fuel injection lines extending from the distributor to each injector. For example, U.S. Pat. No. 4,586,480 to Kobayashi et al. discloses a well known and commonly used distributor comprised of a rotating shaft having a radial supply passage which sequentially aligns with fuel delivery passages corresponding to each engine cylinder. Each period of time defined by the alignment of the supply passage with a delivery passage creates a window of opportunity for injection during which a solenoid valve functions to control the actual amount of fuel delivered to the injector. The rotating shaft also reciprocates to pump the supply fuel through the delivery passages.
A similar type of distributor is disclosed in U.S. Pat. No. 3,598,507 to Voit wherein a rotating shaft contains radially extending supply passages for sequential alignment with delivery passages formed in the distributor housing to deliver fuel to the engine cylinders based on the position of two solenoid operated control valves. Unlike the distributor disclosed in Kobayashi, fuel is pumped through the aligned passages by pump pistons radially disposed in bores formed in the distributor shaft and positioned against a cam ring such that rotation of the shaft causes the pistons to reciprocate through pumping and suction strokes.
Although the distributors disclosed in Kobayashi and Voit both function adequately to deliver metered quantities of fuel to the engine cylinders at low to medium injection pressures, a small amount of leakage occurs between the radially extending passages during each delivery or injection event in the clearance formed between the rotary shaft and the shaft bore formed in the distributor housing within which the shaft rotates. Although this clearance is necessary to permit the distributor shaft to rotate and, in some designs, reciprocate, high pressure injection fuel leaking through this clearance into the adjacent low pressure delivery passages, or other areas of the distributor, makes accurate control of injection metering difficult and/or contributes to excessive parasitic pumping losses. The leakage not only upsets the predictability of the injection characteristics of the delivery passages in alignment but also the injection characteristics of the adjacent delivery passages by pressurizing the passages to an unknown pressure before the respective injection period. Also, the distance between the adjacent delivery passages around the circumference of the shaft is very small due to the compact nature of the distributor and shaft, thereby undesirably creating very short sealing lengths thus increasing leakage.
Moreover, the aforementioned problems, and other complications, caused by the necessary clearances between the distributor shaft and bore, and the associated short sealing lengths, in the conventional rotary distributor are only exacerbated by higher injection pressures required by modem fuel systems. Recent and upcoming legislation resulting from a concern to improve fuel economy and reduce emissions continues to place strict emissions standards on engine manufacturers. In order for new engines to meet these standards, it is necessary to produce fuel injection systems capable of achieving higher injection pressures while maintaining accurate and reliable control of the metering and timing functions. One such high pressure fuel injection system is disclosed in U.S. patent application Ser. No. 057,489 entitled Compact High Pressure Fuel System with Accumulator, commonly assigned to the assignee of the present application wherein an accumulator temporarily stores fuel supplied by a high pressure variable displacement pump for delivery to a distributor via a solenoid controlled three-way valve. This system is capable of achieving extremely high injection pressures in excess of 20,000 psi. However, as with the distributor disclosed in Kobayashi and Voit, the distributor is a conventional rotary distributor using the sequential alignment of a supply passage with a plurality of injection passages to allow delivery of fuel to the injectors of corresponding cylinders. As discussed hereinabove, these distributors rely on a clearance fit between the rotary shaft and the bore, and very short sealing lengths, to isolate the high pressure injection occurring in one delivery passage from the remaining passages. At high injection pressures, fuel leakage through the clearance between the shaft and bore becomes unacceptable. Moreover, it has been found that rotary shafts exposed to high injection pressures are prone to seizures during operation especially when using low viscosity and aromatic fuels.
U.S. Pat. No. 2, 105,100 to Starr discloses a fuel injection system including a distributor having poppet-type distributor valves which are sequentially opened and closed by respective cams to deliver premetered fuel to respective fuel delivery lines leading to respective injectors. These poppet-type valves at least partially overcome the above-noted shortcomings associated with a rotary distributor by providing a valve element which abuts a valve seat to create a positive seal having a longer seal length without the need for leakage causing clearances. However, these poppet-type valves are arranged such that pressurized fuel for injection acts on each valve element in an opening direction against the force of a biasing spring which acts on the valve element in the closing direction. As a result, although the fuel pressure may advantageously assist in the opening of the valve associated with the engine cylinder ready for injection, the fuel pressure also undesirably tends to open the remaining valves which must remain in the sealingly closed position to ensure accurate and predictable control of injection. Consequently, the likelihood of leakage through the poppet-type valve is increased. Although the valve element may be designed to be force balanced to some degree in the closed position in an effort to minimize the opening force caused by the fuel pressure, this requires additional design and manufacturing costs. Moreover, as injection pressures increase, any tendency of the valve to open due to fuel pressure acting on the valve element also increases thus increasing the likelihood of leakage through the valve seat. Also, the biasing spring must be stronger, and possibly larger, than necessary to overcome the tendency of the valve to open. The distributor disclosed in Starr also fails to disclose a means for varying the timing of injection and therefore, could not effectively control injection throughout a wide range of operating conditions to meet the recent and upcoming emissions standards. The opening and closing of the poppet-type distributor valves disclosed in Starr defines the beginning and end of injection, respectively. As a result, the biasing spring must also be of sufficient strength to force the valve element into the closed position at the end of injection against the force of the pressurized fuel.
Consequently, there is a need for a fuel distributor for distributing high pressure fuel through a plurality of distributor valves to the cylinders of an engine which effectively controls the flow of fuel through each of the distributor valves.